Study On The Tribological Propertites Of Porous PI/PTFE Composites

With the continuous development of modern science and technology, polymer matrix composites, which has been widely used, are gradually replacing part of the metal base materials and becoming the trend of the development of materials today. Polyimide as one of the commonly used polymer composites, which has advantages of good chemical stability and high mechanical strength, is widely used in the fields of aviation, aerospace, precision machinery. However, the tribological properties of pure polyimide were poor. In order to improve its tribological properties, some solid lubricants are usually filled and at the same time porous structure with the oil storage ability is prepared. The composites with porous structure has realistic and far-reaching significance in applying the occasions of bad oil supplying and avoiding lubricating oil contamination.In this paper, porous PI/PTFE composites were prepared by filling PTFE into PI-based material and adding pore-forming agent with the method of hot molding process. The optimal combination of the content of pore forming agent and the content of PTFE, molding temperature, molding pressure and heat preservation time was obtained by designing orthogonal test to evaluate the mechanical properties of porous PI/PTFE composites. Micro-porous characteristics of the composites were analyzed by using scanning electron microscopy. The oil absorption and oil retention rate were evaluated through vacuum oil immersion test of porous composites. The influence of the content of pore forming agent, the content of PTFE and different friction working conditions on the friction coefficient and wear rate of PI/PTFE composites was studied. The wear morphology of porous PI/PTFE composites was observed by CSLM to analyze the friction and wear mechanism of the composites.The results showed that the content of pore forming agent had the greatest influence on the mechanical properties of the composites. The pore diameter of the composite increased with the filling of the pore forming agent, while the tensile strength of the composite decreased.The increasing of pore diameter was helpful to increase the oil content of the porous composites, but the oil retention rate decreased.The tribological properties of the composite were significantly improved due to the filling of PTFE. The friction coefficient increased with the increasing content of PTFE, while the wear rate decreased. After oil immersion, the wear surface of porous PI/PTFE composites was mainly adhesion wear. The tribological properties of porous PI/PTFE composites with 12% PTFE and 8% pore forming agent were different under different load and rotational speed,. The optimum operating conditions of the porous composites were medium load and low / medium speed.